Smoking represents a major public health problem worldwide. In the United States alone, smoking is the leading cause of preventable death and is associated with a host of chronic diseases, such as heart disease and lung cancer. Personal and federal financial costs associated with such health consequences remain an economic burden. Despite advances in the area of smoking cessation intervention development, existing interventions leave ample room for improvement. The development of effective strategies to reduce the smoking problem may be best guided by basic research on the bio-behavioral processes underlying smoking maintenance and relapse. Nicotine withdrawal is one major predictor of cessation failure for individuals low in distress tolerance (DT). Specifically, symptoms of acute withdrawal, including anxiety, irritability, and depressed mood, appear responsible for early lapse among those with elevated reactivity and susceptibility to distressing experiential states. Additionally, evidence from both observational and intervention smoking research suggests that early lapsers are at high risk for full smoking remittance, identifying low DT smokers as an at-risk group in need of specialized interventions targeting withdrawal. Reducing nicotine withdrawal-related distress and relapse in low DT smokers may require the regulation of cortisol. Basic research suggests steeper declines in cortisol during withdrawal (2-24 hours post-cessation), explained as an offset effect caused by nicotine deprivation, are directly related to withdrawal symptom intensity, subjective distress, and early lapse. Regular practice of yoga, a mindfulness-based form of physical activity, emerges as a promising strategy for regulating cortisol concentrations, decreasing withdrawal symptoms, and increasing DT, thus promoting smoking cessation success. Whether regular yoga practice can effectively regulate cortisol in smokers with low DT and thereby reduce nicotine withdrawal severity is unknown. Accordingly, the proposed study represents a basic experiment [primarily examining the efficacy of yoga to reduce cortisol and nicotine withdrawal symptoms, while enhancing DT. The secondary aim is to test] cortisol regulation as a putative mediator underlying the effects of an 8 week yoga intervention on nicotine withdrawal symptom severity in low DT smokers. [Finally, the proposed study will obtain effect sizes for the advantage of yoga over waitlist for lapses during a two-week period following a self-guide quit attempt.] By studying key bio-behavioral mechanisms (e.g., cortisol regulation, distress tolerance) underlying nicotine withdrawal, the long-term objectives of the proposed line of research hope to: (1) inform theoretical models of nicotine withdrawal, (2) guide the development of effective alternative interventions for smokers susceptible to lapse and relapse during the first few weeks following a quit attempt, and (3) guide behavioral intervention strategies to regulate cortisol regulation in the context of smoking cessation.